Marowski's chem lab is an unmarked location in the Commonwealth in 2287. It is accessible by a catwalk on the roof of the Four Leaf fishpacking plant, through a security door revealed and opened via a (master) locked terminal.
The main area of the chem lab contains three rooms: an entry room with a broken terminal, a main lab area directly ahead and a small room to the left with beds. One enemy is posted behind the terminal, the other two are in the main lab area. All enemies are immediately hostile. The entry room and the main lab area both contain chemistry stations. Various containers contain a handful of chems.
The main lab room contains a maglocked door with a control terminal which does not require a password. The terminal unlocks the door, leading to the fishpacking plant.
Four hazmat suits can be taken from the chem lab workers when killed.
During the quest Diamond City Blues, Trish states that this place has more loot than what she has in her shipments, however it appears to have significantly less.
Marowski's chem lab only appears in Fallout 4.